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(11) | EP 0 901 643 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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METHOD OF PROVIDING DIFFUSE RISERS ON A FRESNEL LENS DIE VERFAHREN ZUR HERSTELLUNG STREUENDER PRISMENFLANKEN AUF EINER FRESNELLINSENMATRIZE PROCEDE DE CREATION DE PLANS VERTICAUX DE DIFFUSION DANS UN MOULE POUR LENTILLES DE FRESNEL |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
Field of the Invention
Background of the Invention
[0002] Fresnel lenses include a series of optical facets, wherein each optical facet is separated by a riser. That construction provides for a substantially planar lens useful in many different applications.
[0003] One application in which fresnel lenses are particularly useful is in overhead projectors where they help to focus light from beneath the stage and onto the mirror elevated above the stage. In that application, however, light refracted through the risers in the fresnel lens causes what is commonly referred to as "stage glare." Stage glare typically affects the operator of the overhead projector by disrupting their view of the materials on the stage of the projector.
[0004] Attempts to reduce stage glare have involved providing a diffuse surface on the risers to diffuse the light refracted through those surfaces, thereby reducing the glare. The diffuse risers have been provided by chemically etching or attacking the finished lenses or the dies used to form the lenses. Typically the entire lens/die is treated, including the optical facets as well as the risers. After etching, the optical facets are recut or otherwise processed to restore them to a smooth, specular finish while the risers remain etched to provide the desired diffuse surface.
[0005] Etching the lens itself to provide diffusing risers adds significantly to the cost of the lens because each individual lens must be processed separately. Attempts at etching the dies used to form stamped fresnel lenses have reduced stage glare to some degree, but that approach is not compatible with all types of dies used to form lenses. That is particularly true where the materials used to form the dies are not susceptible to etching or, when etched, do not provide a surface that has the desired roughness or diffusing properties.
[0007] DE 38 35 567 discloses a method of providing diffusing risers on a fresnel lens die achieved by applying a rough coating galvanically, chemically or thermally.
Summary of the Invention
[0008] The present invention includes methods of providing diffusing risers on a fresnel lens die having a plurality of optical facets, wherein adjacent optical facets are separated by a riser, according to claim 1.
[0009] Grain refiners and other impurities can be removed from the bath by filtering, typically through activated charcoal and by allowing the temperature of the bath to rise to about 30°C or higher, more preferably about 35°C or higher, and even more preferably about 40°C or higher.
[0010] It may also be helpful to control the rate at which the diffusing layer is deposited by controlling the current density used in the electrodeposition process. It is preferred to control the current density to about 0.022 amps/cm2 (20 amps/ft2) or less, more preferably about 0.016 amps/cm2 (15 amps/ft2) or less, and even more preferably about 0.011 amps/cm2 (10 amps/ft2) or less.
[0011] Methods according to the present invention may also include masking selected portions of the risers during the step of depositing the diffusing layer. The masking can be maintained throughout the deposition process or it may occur during only a portion of the process.
Brief Description of the Drawings
[0012]
Figure 1 is a cross-sectional schematic diagram of a fresnel lens die depicting the optical facets and risers.
Figure 2 is a schematic diagram of one process according to the present invention.
Detailed Description of the Invention
[0013] Figure 1 is a cross-sectional diagram of a typical fresnel lens die 10 including optical facets 12 separated by risers 14. The risers 14 provide the vertical displacement between optical facets 12 that is required to produce a substantially planar lens from the die 10. The die 10 is typically manufactured from metals such as brass, copper, nickel, etc.
[0014] It will be understood that when the die 10 is a "negative" of the desired fresnel lens, it can be used directly to produce a fresnel lens or, alternatively, a "mother" can be electroformed from the die 10 and stampers (also a negative of the desired lens) can then be electroformed from the mothers to produce fresnel lenses. Where the die 10 is a "positive" of the desired fresnel lens, an electroformed copy will be a negative of the lens and can be used to form the desired fresnel lens.
[0015] After the die 10 is formed, the method according to the present invention can be used to provide the desired diffuse risers 14. The basic steps of the method are depicted in the block diagram of Figure 2. First, a diffusing layer is deposited over the entire surface of the die 10, including the optical facets 12 and risers 14. Second, the optical facets 12 are processed to remove the diffusing layer and restore their specular finish while leaving the diffusing layer on the risers 14. The processing typically involves machining, or recutting, the optical facets 12 to remove the diffusing layer from them while leaving the diffusing layer on the risers 14.
[0016] The diffusing layer is formed by electrodepositing a metal such as copper, nickel, zinc, tin, cobalt, etc. Combinations of one or more of the metals may also be used for the diffusing layer. The method of depositing the diffusing layer is electroplating in a bath of electrolyte solution. The bath is substantially free of grain refiners to enhance the diffusing properties of the diffusing layer. If an electrolyte solution prepared with grain refiners is to be used, the bath can be filtered through activated carbon to remove the grain refiners.
[0017] Additionally, the bath can be heated or allowed to heat up during processing to cause degeneration of any grain refiners in the solution. The grain refiners degenerate at elevated temperatures because they are typically organic and, thus, susceptible to heat degeneration. Temperatures of the bath useful in connection with the present invention can range from about 30°C or greater, more preferably about 35°C or greater, and even more preferably about 40°C or greater.
[0018] The current density of the plating process (i.e., amps/plating area) can also play a role in the uniformity of the diffusing layer on the surface of the die. It is preferred that the current density be about 0.022 amps/cm2 (20 amps/ft2) or less, more preferably about 0.016 amps/cm2 (15 amps/ft2) or less, and even more preferably about 0. 011 amps/cm2 (10 amps/ft2) or less. It will be understood that the desire for plating speed, i.e., rate of deposition, will typically be balanced with plating uniformity.
[0019] After the optical facets 12 have been processed, the die 10 can then be electroformed or otherwise duplicated to form mothers or stampers if desired. Alternatively, the die 10 itself could be used to form a fresnel lens.
[0020] In one preferred process, the diffusing layer deposited on the die 10 is matte copper. The process used to electrodeposit the matte copper is described in Example 1 below. The matte finish is provided by electroplating the die 10 in a bath that is substantially free of grain refiners. This produces a finish in the matte copper that is grainier than typically found in electrodeposited copper layers.
Examples
[0021] Features and advantages of the methods according to the present invention are further illustrated in the examples. It is recognized, however, that while the examples serve this purpose, the particular ingredients and amounts used, as well as other conditions and details, are not to be construed in a manner that would unduly limit the scope of this invention.
Example 1
[0022] A fresnel lens die master having a surface area of about 0.2 square meters manufactured of nickel was electroplated with a diffusing layer of matte copper according to the following procedure. An electroplating solution was prepared including copper sulfate (0.21 kg/liter of solution) (copper sulfate pentahydrate sold as Triangle Brand by Phelps Dodge Refining Corporation, El Paso, Texas), sulfuric acid (0.061 kg/liter of solution) (96% pure, reagent grade), chloride (50 PPM), and a surfactant (1 liter of 10% Duponal ME per 757 liters of solution, available from DuPont). The balance of the solution was distilled water. The solution was filtered through a 1 micrometer filter and activated carbon to remove impurities before plating.
[0023] Before electroplating, the die was soaked in MEK/acetone solvent bath to remove oils and other contaminants on the surface of the die. The die was then power washed with a 20% Advanage™ cleaner solution (Advanage™ is available from Austin Diversified Products, Inc., Harvey, Illinois). After power washing, the die was maintained wet in a solution of 20% H2SO4 and 5% Advanage™ (balance distilled water) while it was mounted on the electroplating equipment.
[0024] To insure adhesion of the matte copper diffusing layer, the nickel die was first reverse plated for one minute at 25 amps with the die being the anode. Plating was then commenced after reversing polarity (i.e., the die was the cathode) and plating was carried out for about two hours at 20 amps for a total of 42 amp-hours. During plating, the electroplating solution was held at a temperature of 35°C, the die was rotated in the solution at 3 0 revolutions per minute, the electroplating solution was agitated with a mixer and the solution was recirculated through a 1 micrometer filter at a rate of 114 liters per minute.
Example 2
[0026] A second nickel die essentially identical to the die used in Example 1 was electroplated under the same conditions as set out in Example 1, except that the electroplating was carried out at 42 amps for a total of 42 amp-hours.
[0027] The finished die did not appear as uniformly plated as the die produced according to Example 1.
Example 3
[0028] A copper die with a similar pattern and size as the nickel dies used in Examples 1 and 2 was plated with matte copper according to the process described in Example 1 with the following exceptions: the temperature of the bath during plating was 40°C; the plating was carried out for about 40 minutes at 13-15 amps for a total of 11 amp-hours.
[0029] The resulting die had a uniform satin appearance. When a nickel electroform was produced using the die, virtually none of the matte copper was removed by the electroformed copy.
Example 4
[0030] A copper die was electroformed according to Example 3, with the following exception: during plating, a mask was placed with the logo of Minnesota Mining and Manufacturing Company ("3M") over the die for about one-half of the total plating time. The logo was provided of a magnetic material that adhered to the nickel substrate on which the copper surface was mounted. Because no further plating occurred in the area underneath the mask after its placement, the plating thickness was reduced in the area covered by the mask, resulting in the logo being transferred to the die. Lenses that were ultimately manufactured from this die also exhibited the logo when viewed from an angle, i.e., not normal to the plane of the lens.
1. A method of providing diffusing risers on a fresnel lens die having a plurality of
optical facets, wherein adjacent optical facets are separated by a riser, the method
comprising the steps of:
a) depositing a diffusing layer on the plurality of optical facets and the risers, wherein the depositing comprises electrodepositing a layer of metal chosen from the group consisting of copper, nickel, zinc, cobalt, tin, and combinations thereof, and further wherein the electrodepositing is performed in a bath substantially free of grain refiners; and
b) selectively removing the diffusing layer from the plurality of optical facets, wherein the diffusing layer remains substantially intact on the risers.
2. A method according to claim 1, wherein the step of depositing further comprises depositing
the diffusing layer on a die having generally concentric optical facets.
3. A method according to claim 1, wherein the step of depositing further comprises depositing
the diffusing layer on a die having generally parallel optical facets.
4. A method according to any of claims 1-3, further comprising a step of passing the
bath through activated charcoal.
5. A method according to any of claims 1-4, further comprising a step of heating the
bath to a temperature of about 30°C or higher.
6. A method according to any of claims 1-4, further comprising a step of heating the
bath to a temperature of about 35°C or higher.
7. A method according to any of claims 1-4, further comprising a step of heating the
bath to a temperature of about 40°C or higher.
8. A method according to any of claims 1-7, further comprising masking selected portions
of the risers during the step of depositing the diffusing layer.
9. A method according to any of claims 1-7, further comprising masking selected portions
of the risers during a portion of the time during which the step of depositing is
being performed.
10. A method according to any of claims 1-9, wherein the step of depositing further comprises
passing electrical energy through the die having a current density of about 0.022
amps/cm2 or less.
11. A method according to any of claims 1-9, wherein the step of depositing further comprises
passing electrical energy through the die having a current density of about 0.016
amps/cm2 or less.
12. A method according to any of claims 1-9, wherein the step of depositing further comprises
passing electrical energy through the die having a current density of about 0.011
amps/cm2 (10 amps/ft2) or less.
1. Verfahren zur Herstellung streuender Flanken auf einer Fresnellinsenmatrize mit mehreren
optischen Facetten, wobei benachbarte optische Facetten durch eine Flanke getrennt
sind, wobei das Verfahren die folgenden Schritte aufweist:
a) Abscheiden einer Streuschicht auf die mehreren optischen Facetten und die Flanken, wobei das Abscheiden das elektrochemische Abscheiden einer Schicht aus Metall aufweist, das aus der Gruppe ausgewählt ist, die aus Kupfer, Nickel, Zink, Cobalt, Zinn und deren Kombinationen besteht, und wobei ferner das elektrochemische Abscheiden in einem Bad durchgeführt wird, das im wesentlichen frei von Kornverfeinerern ist; und
b) selektives Entfernen der Streuschicht von den mehreren optischen Facetten, wobei die Streuschicht auf den Flanken im wesentlichen intakt bleibt.
2. Verfahren nach Anspruch 1, wobei der Schritt des Abscheidens ferner das Abscheiden
der Streuschicht auf eine Matrize aufweist, die allgemein konzentrische optische Facetten
hat.
3. Verfahren nach Anspruch 1, wobei der Schritt des Abscheidens ferner das Abscheiden
der Streuschicht auf eine Matrize aufweist, die allgemein parallele optische Facetten
hat.
4. Verfahren nach einem der Ansprüche 1 bis 3, ferner mit einem Schritt des Durchleitens
des Bads durch Aktivkohle.
5. Verfahren nach einem der Ansprüche 1 bis 4, ferner mit einem Schritt des Erwärmens
des Bads auf eine Temperatur von mindestens etwa 30 °C.
6. Verfahren nach einem der Ansprüche 1 bis 4, ferner mit einem Schritt des Erwärmens
des Bads auf eine Temperatur von mindestens etwa 35 °C.
7. Verfahren nach einem der Ansprüche 1 bis 4, ferner mit einem Schritt des Erwärmens
des Bads auf eine Temperatur von mindestens etwa 40 °C.
8. Verfahren nach einem der Ansprüche 1 bis 7, ferner mit dem Maskieren ausgewählter
Abschnitte der Flanken während des Schritts des Abscheidens der Streuschicht.
9. Verfahren nach einem der Ansprüche 1 bis 7, ferner mit dem Maskieren ausgewählter
Abschnitte der Flanken während eines Abschnitts der Zeit, in der der Schritt des Abscheidens
durchgeführt wird.
10. Verfahren nach einem der Ansprüche 1 bis 9, wobei der Schritt des Abscheidens ferner
das Durchleiten elektrischer Energie durch die Matrize mit einer Stromdichte von höchstens
etwa 0,022 A/cm2 aufweist.
11. Verfahren nach einem der Ansprüche 1 bis 9, wobei der Schritt des Abscheidens ferner
das Durchleiten elektrischer Energie durch die Matrize mit einer Stromdichte von höchstens
0,016 A/cm2 aufweist.
12. Verfahren nach einem der Ansprüche 1 bis 9, wobei der Schritt des Abscheidens ferner
das Durchleiten elektrischer Energie durch die Matrize mit einer Stromdichte von höchstens
etwa 0,011 A/cm2 (10 A/ft2) aufweist.
1. Procédé de création de plans verticaux de diffusion dans un moule pour lentilles de
fresnel comprenant une pluralité de facettes optiques, dans lequel les facettes optiques
adjacentes sont séparées par un plan vertical, le procédé comprenant les étapes consistant
à :
a) déposer une couche de diffusion sur la pluralité des facettes optiques et des plans verticaux, dans lequel l'étape consistant à déposer la couche de diffusion comprend l'étape consistant à déposer par électrodéposition une couche de métal choisi à partir du groupe comprenant le cuivre, le nickel, le zinc, le cobalt, l'étain, ainsi que des combinaisons de ceux-ci et dans lequel, en outre, l'étape consistant à déposer par électrodéposition la couche de métal est réalisée dans des bains d'agents de raffinage sensiblement exempts de grains ; et
b) éliminer de façon sélective la couche de diffusion de la pluralité des facettes optiques, dans lequel la couche de diffusion demeure sensiblement intacte sur les plans verticaux.
2. Procédé selon la revendication 1, dans lequel l'étape consistant à déposer la couche
de diffusion comprend en outre l'étape consistant à déposer la couche de diffusion
dans un moule comprenant généralement des facettes optiques concentriques.
3. Procédé selon la revendication 1, dans lequel l'étape consistant à déposer la couche
de diffusion comprend en outre l'étape consistant à déposer la couche de diffusion
dans un moule comprenant généralement des facettes optiques parallèles.
4. Procédé selon l'une quelconque des revendications 1 à 3, comprenant en outre une étape
consistant à faire passer le bain à travers du charbon actif.
5. Procédé selon l'une quelconque des revendications 1 à 4, comprenant en outre une étape
consistant à chauffer le bain à une température de 30°C environ ou plus.
6. Procédé selon l'une quelconque des revendications 1 à 4, comprenant en outre une étape
consistant à chauffer le bain à une température de 35°C environ ou plus.
7. Procédé selon l'une quelconque des revendications 1 à 4, comprenant en outre une étape
consistant à chauffer le bain à une température de 40°C environ ou plus.
8. Procédé selon l'une quelconque des revendications 1 à 7, comprenant en outre une étape
consistant à masquer des parties sélectionnées des plans verticaux au cours de l'étape
consistant à déposer la couche de diffusion.
9. Procédé selon l'une quelconque des revendications 1 à 7, comprenant en outre une étape
consistant à masquer des parties sélectionnées des plans verticaux au cours d'une
partie de la durée pendant laquelle l'étape consistant à déposer la couche de diffusion
est réalisée.
10. Procédé selon l'une quelconque des revendications 1 à 9, dans lequel l'étape consistant
à déposer la couche de diffusion comprend l'étape consistant à faire passer une énergie
électrique à travers le moule ayant une densité de courant de 0,022 amp/cm2 environ ou moins.
11. Procédé selon l'une quelconque des revendications 1 à 9, dans lequel l'étape consistant
à déposer la couche de diffusion comprend l'étape consistant à faire passer une énergie
électrique à travers le moule ayant une densité de courant de 0,016 amp/cm2 environ ou moins.
12. Procédé selon l'une quelconque des revendications 1 à 9, dans lequel l'étape consistant
à déposer la couche de diffusion comprend l'étape consistant à faire passer une énergie
électrique à travers le moule ayant une densité de courant de 0,011 amp/cm2 (10 amp/ft2) environ ou moins.